How Does Intermittent Fasting Affect the Brain?

Camille Freking, MS Translational Pharmacology and Clinical Research
How Does Intermittent Fasting Affect the Brain?

Dieting has become increasingly common over the years. As health education and obesity awareness have become more prevalent, so has the number of people looking to manage their weight. 

The CDC found that roughly 17.4 percent of U.S. adults over 20 were on a specialized diet from 2017 to 2018. For comparison, only 14.3 percent of American adults had some kind of dietary restriction from 2007 to 2008.

One of the most challenging things about starting a diet is that many choices exist. Some people follow the strict low-carb, high-fat diet that’s more commonly known as keto. Others are content with following a gluten-free diet. Another option is to create your meals using the Mediterranean diet

In recent years, one of the growing trends in dieting doesn’t involve a particular diet. The “non-diet” of intermittent fasting isn’t about what you eat but when you’re eating it. If you’re one of the millions of Americans that struggle with following a diet, intermittent fasting may be worth a try. 


What Is Intermittent Fasting?

Everyone will intermittently fast multiple times throughout the day. The term “breakfast” derives from breaking your overnight fast. The difference with intermittent fasting for weight loss is that you’ll fast more strategically. By fasting more often, you can train your body to operate differently. 

The idea isn’t to limit your caloric intake as many diets recommend. Instead, the goal is to mirror the eating habits of our ancestors. Food was hard to come by in the original days of human history, and it could be a long time between meals. 

As a result, the human body adjusted to these periods of food instability by altering its metabolic rate. Forcing the body into a state of metabolic switching is how intermittent fasting can help you lose weight.

There are many different forms of intermittent fasting, but they can most easily be broken down into three categories:


Time Restricted Eating

Time-restricted eating is the most popular form of intermittent fasting and the easiest for beginners. The goal is to limit the meals, snacks, and beverages to calorie restriction at specific daily windows. 

For example, a 16:8 ratio would mean you could only ingest calories for eight hours daily. For the remaining 16 hours, you could only ingest water or other fluids with no calories. The most common ratios are 12:12, 14:10, 16:8, 18:6, and 20:4. It’s best to start with a larger window for eating and slowly shrink it as you become more comfortable with fasting. 


The second most common option is to follow the 5:2 intermittent fasting plan. This requires following a heavily calorie-restricted diet for two days each week. It’s up to you if you would rather make these days consecutive (such as the weekend) or split them up. 

On fasting days, you would only be allowed between 500 and 600 calories and non-calorie liquids. The other five days would have no such restrictions, and you could eat regularly. 


Alternate Day Fasting

The last variety of intermittent fasting is a more intense version of the 5:2 method. For this option, you would be fasting every other day and only permitted 25 percent of your recommended daily caloric intake, between 400 and 750 calories

You can drink fluids as long as they have no calories, but the amount of food you eat would be severely limited. You can eat whatever you want the following day, but the fasting state will resume the next day. 


What Happens to Your Body When You Fast?

Modern diets typically involve eating every two to four hours or so. It might be something light (such as an afternoon snack for extra energy) or a meal with multiple courses. Either way, the calories are fairly consistent and arrive regularly. 

As mentioned earlier, this isn’t exactly the type of diet that our ancestors followed. It could be days between meals which meant their bodies needed to find a way to survive without.

You probably already know that the body holds on to excess fat and stores it for later use. These deposits cause your scale to increase and your waistline to expand. After about six hours of fasting, the brain starts to release human growth hormone (HGH), telling the body to use fat stores for energy

Autophagy then begins, cleaning up and recycling unused cells along with leftover nutrients from previous meals. The so-called “cleansing” of your body is one of the primary benefits of fasting. 

The easiest way to understand the effect that fasting has on the body is to use your refrigerator as a stand-in. Let’s say you have leftovers in the fridge and other things you could use to prepare a meal

A modern diet would be like going out for pizza. Fasting would be using the food you already have to eat for the day. The refrigerator would be cleaned out, you would no longer be hungry, you’d save a few bucks on dinner, and you wouldn’t waste any food. 


Does Intermittent Fasting Help You Lose Weight?

When followed properly, losing weight through intermittent fasting can be fairly easy. A review of 40 studies involving intermittent fasting found the typical weight loss after 10 weeks was between seven and 11 pounds

These results are roughly the same as diets based on caloric restriction. However, some results suggest that intermittent fasting might be more effective at reducing inflammation and improving blood pressure, cholesterol levels, and sugar/insulin sensitivity.

It’s important to note that intermittent fasting is most effective at weight loss when you’re careful about your food intake. Like almost every other health guideline, it’s highly recommended to avoid ingesting too much sugar when intermittent fasting. Ideally, you can stick to lean proteins, fruits, vegetables, nuts, seeds, and whole grains whenever you eat.


What Effect Does Intermittent Fasting Have on the Brain?

The most popular attribute of intermittent fasting is that it can help people lose weight. However, weight loss isn’t the only advantage of intermittent fasting, as it might also benefit your brain health. 

A lot remains unclear regarding the positive effects of intermittent fasting on the human brain. With that said, these are a few of the preliminary health benefits provided by tests involving animal models: 


It Increases BDNF Levels

BDNF (brain-derived neurotrophic factor) is essential for neuron resilience and growth. Intermittent fasting has been shown to increase BDNF in the brain at a similar rate to regular exercise. The upregulation of BDNF can protect the brain from oxidative damage, lower inflammation, and eliminate waste byproducts. 

BDNF stimulates the growth and differentiation of neurons and synapses, which can help to maintain cognitive function. For example, stronger brain cells with more efficient communication can go a long way toward preventing plaque build-ups associated with age-relatedneurological disorders. 

Additionally, the enhanced neuroplasticity provided by BDNF might also be beneficial for supporting learning abilities and memory recall. The hippocampus, cortex, and basal forebrain most often experience the effects of BDNF. Each region is vital for memory, learning, mental health, and general brain cognition.


It Improves Mitochondrial Function

Most people learn that the mitochondria are the “powerhouse of the cell” in school. The mitochondria produce energy within the cell, so this simplified definition is quite accurate. 

In addition to energy metabolism, the mitochondria of brain cells are responsible for calcium ion regulation, axonal/dendritic development, axonal regeneration, and synaptic function. In short, the brain relies on efficient mitochondrial function in as many neurons as possible. 

As mentioned earlier, the cells in your body must adapt and become more efficient at processing energy whenever you fast. The process is known as mitochondrial biogenesis, which involves producing new mitochondria and repairing damaged ones

These “new and improved” mitochondria are more effective at processing energy, preventing brain cell hyperactivity. As a result, brain cells are better protected from damage, can communicate more coherently, and become more efficient at producing dopamine. 


Fasting May Provide a Feast of Benefits

Intermittent fasting is currently one of the most popular ways to lose weight. With intermittent fasting, you choose these fasting periods strategically rather than simply fasting during sleeping hours. 

The longer periods of fasting can force your body to adapt and start using stored nutrients as an energy source. Within a few weeks, you could start to experience noticeable weight loss. Shedding extra weight isn’t the only benefit of intermittent fasting. 

It can also have a profound effect on your brain function. Most of the effects are similar to those of the ketogenic diet, including more ketone production, higher BDNF levels, and improved mitochondrial function. The difference is that the keto diet can be challenging to follow. Instead of redesigning your diet to embrace keto, you can increase your fasting periods. 

It’s important to note that intermittent fasting isn’t recommended for everyone. It can be dangerous to attempt intermittent fasting if you have type 1 diabetes, are underweight, have an eating disorder, or are at risk of malnutrition. 

If you decide to try intermittent fasting, you can start with a beginner eating pattern and slowly work your way up to the more extreme fasting schedules. Remember that the goal is to retrain your body to be more efficient and not starve it into shock. It’s best to only increase your periods of fasting once your body has adjusted to the newest fasting regimen. 

Disclaimer: The information provided in this post regarding fasting is intended for educational purposes only and should not be considered as medical advice. Fasting can have varying effects on individuals, and it is crucial to consult your healthcare professional before undertaking any fasting regimen. Your doctor will evaluate your medical history, current health condition, and any medications you may be taking, in order to determine whether fasting is appropriate for you. Always follow the recommendations of your healthcare professional to ensure your safety and well-being.



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Pleiotropic Mitochondria: The Influence of Mitochondria on Neuronal Development and Disease | Journal of Neuroscience

Brain-Derived Neurotrophic Factor and Its Clinical Implications | PMC

Putting Cells in Motion: Advantages of Endogenous Boosting of BDNF Production | NCBI Bookshelf

Fasting for 20 H Does Not Affect Exercise-Induced Increases in Circulating Bdnf in Humans | The Journal of Physiology | Wiley Online Library

Oxidative Metabolism: Glucose Versus Ketones | Ncbi Bookshelf

Diet Review: Intermittent Fasting for Weight Loss | The Nutrition Source | Harvard School of Public Health

The Effect of Fasting on Human Metabolism and Psychological Health | PMC

How Many Calories Should You Eat in a Day? The USDA’s Guidelines for Men, Women and Children | USA Today

The Evolution of Diet | National Geographic

Why Do We Call It Breakfast? | Wonderopolis

Unexpected Clues Emerge About Why Diets Fail | Scientific American

Mediterranean Diet | Cleveland Clinic

Special Diets Among Adults: United States, 2015–2018 | CDC

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